SAM returning value class crashes compiler

Foo.scala

package sam

// scala 2.12.3
object SonOfSAM {
  val long:SonOfSAM[Long] = i => new Foo(i)
}
trait SonOfSAM[A]{
  def foo(a:A):Foo
}

class Foo(val toLong:Long) extends AnyVal

output.txt

λ scalac Err.scala
warning: an unexpected type representation reached the compiler backend while compiling Err.scala: ErasedValueType(class Foo, Long). If possible, please file a bug on https://github.com/scala/bug/issues.
scala.MatchError: ErasedValueType(class Foo, Long) (of class scala.reflect.internal.Types$UniqueErasedValueType)
	at scala.tools.nsc.backend.jvm.BTypesFromSymbols.typeToBType(BTypesFromSymbols.scala:220)
	at scala.tools.nsc.backend.jvm.BTypesFromSymbols.methodBTypeFromMethodType(BTypesFromSymbols.scala:154)
	at scala.tools.nsc.backend.jvm.BTypesFromSymbols.methodBTypeFromSymbol(BTypesFromSymbols.scala:145)
	at scala.tools.nsc.backend.jvm.BTypesFromSymbols.$anonfun$buildInlineInfoFromClassSymbol$6(BTypesFromSymbols.scala:604)
	at scala.collection.Iterator$$anon$11.nextCur(Iterator.scala:473)
	at scala.collection.Iterator$$anon$11.hasNext(Iterator.scala:479)
	at scala.collection.Iterator.foreach(Iterator.scala:929)
	at scala.collection.Iterator.foreach$(Iterator.scala:929)
	at scala.collection.AbstractIterator.foreach(Iterator.scala:1417)
	at scala.collection.TraversableOnce.toMap(TraversableOnce.scala:316)
	at scala.collection.TraversableOnce.toMap$(TraversableOnce.scala:314)
	at scala.collection.AbstractIterator.toMap(Iterator.scala:1417)
	at scala.tools.nsc.backend.jvm.BTypesFromSymbols.buildInlineInfoFromClassSymbol(BTypesFromSymbols.scala:637)
	at scala.tools.nsc.backend.jvm.BTypesFromSymbols.buildFromSymbol$1(BTypesFromSymbols.scala:536)
	at scala.tools.nsc.backend.jvm.BTypesFromSymbols.buildInlineInfo(BTypesFromSymbols.scala:541)
	at scala.tools.nsc.backend.jvm.BTypesFromSymbols.setClassInfo(BTypesFromSymbols.scala:458)
	at scala.tools.nsc.backend.jvm.BTypesFromSymbols.classBTypeFromSymbol(BTypesFromSymbols.scala:134)
	at scala.tools.nsc.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.genPlainClass(BCodeSkelBuilder.scala:94)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase$Worker1.visit(GenBCode.scala:190)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase$Worker1.$anonfun$run$1(GenBCode.scala:139)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase$Worker1.run(GenBCode.scala:139)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.buildAndSendToDisk(GenBCode.scala:381)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.run(GenBCode.scala:350)
	at scala.tools.nsc.Global$Run.compileUnitsInternal(Global.scala:1431)
	at scala.tools.nsc.Global$Run.compileUnits(Global.scala:1416)
	at scala.tools.nsc.Global$Run.compileSources(Global.scala:1412)
	at scala.tools.nsc.Global$Run.compile(Global.scala:1515)
	at scala.tools.nsc.Driver.doCompile(Driver.scala:35)
	at scala.tools.nsc.MainClass.doCompile(Main.scala:24)
	at scala.tools.nsc.Driver.process(Driver.scala:55)
	at scala.tools.nsc.Driver.main(Driver.scala:68)
	at scala.tools.nsc.Main.main(Main.scala)
error: Error while emitting Err.scala
ErasedValueType(class Foo, Long) (of class scala.reflect.internal.Types$UniqueErasedValueType)
java.lang.AssertionError: assertion failed: ClassBType.info not yet assigned: Lsam/SonOfSAM$;
	at scala.tools.nsc.backend.jvm.BTypes$ClassBType.info(BTypes.scala:891)
	at scala.tools.nsc.backend.jvm.BTypes$ClassBType.isNestedClass(BTypes.scala:951)
	at scala.tools.nsc.backend.jvm.analysis.BackendUtils$Collector.getClassIfNested(BackendUtils.scala:297)
	at scala.tools.nsc.backend.jvm.analysis.BackendUtils$NestedClassesCollector.visitInternalName(BackendUtils.scala:517)
	at scala.tools.nsc.backend.jvm.analysis.BackendUtils$NestedClassesCollector.visitInternalNameOrArrayReference(BackendUtils.scala:526)
	at scala.tools.nsc.backend.jvm.analysis.BackendUtils$NestedClassesCollector.$anonfun$visit$3(BackendUtils.scala:504)
	at scala.tools.nsc.backend.jvm.analysis.BackendUtils$NestedClassesCollector.$anonfun$visit$3$adapted(BackendUtils.scala:486)
	at scala.collection.Iterator.foreach(Iterator.scala:929)
	at scala.collection.Iterator.foreach$(Iterator.scala:929)
	at scala.collection.AbstractIterator.foreach(Iterator.scala:1417)
	at scala.collection.IterableLike.foreach(IterableLike.scala:71)
	at scala.collection.IterableLike.foreach$(IterableLike.scala:70)
	at scala.collection.AbstractIterable.foreach(Iterable.scala:54)
	at scala.tools.nsc.backend.jvm.analysis.BackendUtils$NestedClassesCollector.visit(BackendUtils.scala:486)
	at scala.tools.nsc.backend.jvm.analysis.BackendUtils.collectNestedClasses(BackendUtils.scala:309)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase$Worker2.setInnerClasses(GenBCode.scala:253)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase$Worker2.run(GenBCode.scala:268)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.buildAndSendToDisk(GenBCode.scala:384)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.run(GenBCode.scala:350)
	at scala.tools.nsc.Global$Run.compileUnitsInternal(Global.scala:1431)
	at scala.tools.nsc.Global$Run.compileUnits(Global.scala:1416)
	at scala.tools.nsc.Global$Run.compileSources(Global.scala:1412)
	at scala.tools.nsc.Global$Run.compile(Global.scala:1515)
	at scala.tools.nsc.Driver.doCompile(Driver.scala:35)
	at scala.tools.nsc.MainClass.doCompile(Main.scala:24)
	at scala.tools.nsc.Driver.process(Driver.scala:55)
	at scala.tools.nsc.Driver.main(Driver.scala:68)
	at scala.tools.nsc.Main.main(Main.scala)
error: Error while emitting sam/SonOfSAM
assertion failed: ClassBType.info not yet assigned: Lsam/SonOfSAM$;
one warning found
two errors found